Presently, communication service providers, such as AT&T, offer high-speed Asynchronous Transport Mode (ATM) Virtual Private Network (VPN) service to customers. Each ATM-based VPN customer utilizes one or more Permanent Virtual Circuits (PVCs) to route data among different locations (endpoints), each typically located at a separate edge of an ATM network. In practice, traffic originating at an endpoint passes to an edge device on the ATM network for transmission to the network core, which in turn, transmits such traffic to an edge device serving the destination end point. While the edge devices may run one or more different protocols, including ATM or Frame Relay, the network core typically utilizes the ATM protocol. In this environment, ATM PVCs constitute a point-to-point network topology.
Currently, there exists a large embedded base of Ethernet Local Area Networks (LANs). Advances in Ethernet technology have led to the development of Metropolitan Area Networks (MANs) that afford access to the Internet and some limited access to VPNs. Ethernet-based MANs offer significant cost advantages on a per port basis, as compared to Frame Relay and ATM networks. Many VPN customers would like the opportunity to use an Ethernet-based MAN to access their ATM-based VPNs but have not had the ability to do so because of interworking issues. The protocol associated with Ethernet is different than that associated with ATM. Ethernet is a broadcast protocol within level 2 (the data link layer) of the well-known 7-layer OSI model, whereas ATM and Frame Relay is a point-to-point circuit-type protocol within level 2. Ethernet is designated as a broadcast protocol within level 2 because information in an Ethernet network travels in both directions and passes by all devices on the path. A device that recognizes the information intended for itself (as opposed to another device) will pull the information from the network.
U.S. patent application Ser. No. 10/016,019, filed Dec. 12, 2001 in the names of Stephen L. Holmgren, David Kinsky, John Babu Medamana and Mateusz Szela, and assigned to AT&T (incorporated by reference therein) describes a technique for interworking Ethernet to ATM networks. An interworking facility receives frames from a first network that are destined for the second network. Each such frame destined for the second network includes not only the payload, but also a destination address indicative of the endpoint in the second network destined to receive the information in the payload. The destination address is obtained by initially resolving the destinations available to the source, including those available through the second network. In practice, the interworking facility establishes a set of pseudo addresses in a format compatible with the first network that correspond to destinations in the second network so that the source can address an information frame using its own protocol for a destination that actually lies in the second network without concerning itself with the protocol employed in the second network. In the case where the first information frame comes from a source in an Ethernet-based network, the first information frame will have a Virtual Local Area Network (VLAN) tag associated with the address of the destination. On the other hand, if the information frame comes from a source in an ATM network, the frame will include a VPN Virtual Circuit Identifier (VCI), herein after referred to as a Permanent Virtual Circuit (PVC) that corresponds to the address of (e.g., the network path to) the destination in a format compatible with the ATM network, even though the destination lies in another network having a different protocol.
Upon receipt of the first information frame at the interworking facility, the facility forms a second frame (which includes the payload) in a format compatible with the second network. The interworking facility maps destination address of the first frame to a second destination address compatible with the second network. Thus, for example, the VLAN tag in an originating Ethernet frame is mapped to a VPN PVC in an ATM frame and vice versa. Mapping the destination address from a format compatible with the first information frame to a format compatible with the second information frame allows routing of the second frame, including the information embodied in its payload, to the destination.
As described above, the interworking technique of the aforementioned U.S. patent application Ser. No. 10/016,019 permits interworking of Ethernet to Frame Relay or ATM networks by mapping Ethernet VLANs to ATM PVCs and vice versa. While this technique works well, most large Frame Relay and ATM customers typically enjoy hundreds if not thousands of PVCs per access link whereas the VLAN ID space within an Ethernet frame is limited to 12 bits (4096) values, thus limiting mapping.
Thus, there is a need for a technique for expanding the VLAN ID space to enhance Ethernet-to-ATM interworking.